A locking of the operating lever with the valve body by means of a padlock in order to prevent the uncontrolled opening or closing of the valve for purposes of safety and against tampering of the unit, has already been proposed for such valves. A locking element is wedged onto the operating lever, and according to the known method. When it is secured by means of the padlock, the locking element only achieves a bond of the lever with the valve body for preventing its rotation in any direction up to the time that the padlock is not removed and the element is shifted into the inoperative position. Nevertheless, such an element, even though it is functional with regard to the locking of the lever, has the serious shortcoming of leaving the means, usually a nut, which secures the lever itself on the working pin of the valve obturator, uncovered, and at any rate, exposed. Therefore, although locked in the closing or opening position, the lever can be literally disassembled by removing the nut, and therefore, it leaves open a possibility of tampering with the valve, since, with the lever removed, the valve obturator can be rotated.